The pregnancy is divided into three trimesters of about 13 weeks each. In each quarter there are a series of developmental milestones in the fetus and changes in the mother that lead to the birth of the baby around the 40th week of gestation.
The first trimester of pregnancy
The first quarter goes from week 1 to 13. In these weeks, the conception and implantation of the embryo take place between the third and fourth week of pregnancy and, when this has occurred, the pregnancy begins.
During these first weeks organogenesis occurs, that is, the creation of the main organs of the fetus, so, by week 12, it already has all the main organs formed and beginning to perform its functions, although they have to finish mature in the following weeks. Thus, the heart is already divided into the 4 chambers and beats; the brain has begun to divide into its main parts and create neurons; The digestive system has all its organs and some begin to function; etc.
At the end of week 13, the fetus is about 8 cm and is already moving throughout the uterus, although you still cannot notice it.
As for the changes in the mother, these are the most complicated weeks for many due to the symptoms of the first trimester: nausea and vomiting, tiredness, sleep, abdominal pains, slight bleeding, dizziness, etc. The good news is that these discomforts are decreasing at the end of this quarter and the second begins.
As for this quarter’s tests, you will have a blood and urine test around week 8 to check that all your levels are adequate. They will also do the triple screening test between week 10 and 12 , which consists of a blood test in which the values of two biochemicals are detected: that of the beta fraction of the pregnancy hormone (hCG) and the values of the placental protein associated with pregnancy (PAPP-A); These values are used to calculate the probability that the fetus has some chromosomal abnormality such as Down syndrome or Edwards syndrome. Finally, at week 12, they will perform an ultrasound scan to see if the fetus is well placed if it is one or more fetuses, the position of the placenta, its size, the formation of all organs and measure the nuchal fold to the calculation of probabilities of chromosomal abnormalities.
The second trimester of pregnancy
The second trimester goes from week 14 to 27 and there are many changes in the fetus that goes from measuring about 8 cm to measuring 34 cm and weighing almost a kilo. Their organs mature in this week and, with the exception of the brain and lungs, they are fully developed and ready for birth. Therefore, if the baby was born in week 27, it would already have an 80% chance of survival.
In addition, the baby’s movements have become increasingly controlled and intense, so you can begin to notice how he moves from the 18-20 week, a moment without a doubt magical and special.
As for the mother, the discomforts of the first trimester resulted in a calmer second trimester, although it is normal to occasionally have certain symptoms such as burning, constipation, gas or pain in the abdominal area due to stretching of the uterus and the ligaments that hold it. And at the end of the trimester, it is normal that you begin to feel more tired and heavy due to the increase in the size of the uterus and that you begin to experience Braxton Hicks contractions more and more often, contractions of preparation of the uterus for childbirth.
As for the tests, at week 20 you will have a morphological ultrasound to check if the fetus has formed correctly, in addition to confirming the sex and assess whether the placenta and the umbilical cord are correctly formed or there is a problem in them. You will also be tested again for blood and urine and the glucose test at week 24 to see if you suffer or not gestational diabetes.
The third trimester of pregnancy
This quarter goes from week 28 to 40, although it can be extended until 42 if the birth does not occur before. In these weeks the fetus finishes maturing its lungs and brain, a milestone that reaches around week 35 and continues to gain weight and grow to reach 50 cm and 3.5 kilos on average, although the weight and height final depends on genetics, sex, growth throughout pregnancy, etc.
In addition, around week 32 of pregnancy is placed face down, in a position to be born. Only some babies remain on their backs or are placed transversely, which will make vaginal delivery difficult.
From week 37 the baby is considered full-term, so it can be born at any time without being premature, so the mother should be attentive to the signs that indicate that the birth has begun : rupture of the amniotic bag or regular contractions , intense, increasingly frequent and lasting that do not cease in two hours.
On the other hand, it is normal for the most to feel more tired and heavy in these weeks, so you should try to rest and be calm, with everything ready for when the time comes.
As for the third-trimester tests, around the 33rd week, the last blood and urine tests and an ultrasound are done to verify that the growth of the fetus is adequate and its posture for delivery. At week 35, a vaginal smear is done to check if the mother has a presence in the streptococcus B vagina and antibiotics are needed at birth. And from week 37 in some centers and 39-40 in others, fetal monitors are done to check fetal well-being and uterine activity to see if labor is necessary to induce labor.